Underfloor duct



Jam 27, 194:2-v w. c. ROBINSON E1- AL v 2,271,465

UNDERFLOOR DUCT Filed June l19, 1939 ar/"OWS Jhd/'Cate adjustab//fg Patented Jan. 27, 1942 UNDERFLOOR DUCT william o. Robinson and James M. G. Fullinap, Sewickley, Pa., assignors to National Electric Products Corporation, a corporation of Dela- Wavre Application June 19, 1939, Serial No. 279,864

3 Claims.

Our invention relates to underfloor duct systems, systems of conduits or ducts which are embedded in concrete floors to provide raceways and housings for electrical service wires.

In systems of this sort, branch connections are made through the floor to the embedded conduits, and, in order to facilitate the making of such branch connections, access elements are provided on the conduits. The usual access element consists in a cup or tube of metal that is seated and secured upon the upper face of the conduit before the concrete is laid or cast. When the oor structure has been completed, the cup or tube provides a vertical bore or pocket between the face of the floor and the top wall of the conduit. If it becomes necessary to make a branch connection through the floor at this point, access to the conduit is readily obtained, by breaking through the oor at the mouth of the access element, and then drilling, or otherwise providing, a passage in the top wall of the buried conduit.

It has been customary to provide the access elements in such profusion in the duct systems that, no matter where a connection might in the future be desired, the need can be met. The means for positioning and securing the access elements in the system have usually consisted in screws, or other devices, provided in the factory on the conduit in longitudinally spaced-apart relation. This factory standardization of the spacing at which the access elements may be applied to the conduit has more or less curtailed the adaption of the equipment to the various particular conditions met in the field, and the result has been that in particular installations more access elements have been installed than have been actually needed. Indeed, over a period of years experience has shown that in some cases only one out of every twenty of the installed access elements has come into use. Furthermore, it has been found that in this wasteful practice many access elements are provided at points where it is practically certain that no branch connection will ever be required, such as in the floors of corridors, public reception rooms, and the like.

The object of our invention is to correct this wasteful practice, and the invention consists in new and useful improvements to such end. More particularly, the invention consists in certain renements and elaborations in the structure of access elements, by virtue of which:

(1) It becomes more feasible to provide access elements atthe points of probable service, and

only at such points, irrespective of the space in- 55 mtting adjustmentafter application, and a more tervals between any two or more elements that have been applied on a given reach of conduit;

(2) It becomes more practical to apply the access elements to the conduits in the field, without the aid of special tools, and it becomes more feasible to apply the elements at any desired points on conduits, particularly metal conduits,

that have in no way been `structurally modified orv elaborated to receive the elements;

(3) It becomes easier to provide a clean and well-defined opening in the upper wall of a conduit, particularly a metal conduit, to gain the desired access at precisely the desired point;

(4) It becomes possible, during the installation of the conduit, to adjust and vary the positions of the applied access elements at will, preferably without removing the elements from the conduit and without loss of the desired rigidity and security of assembly against unintended or accidental movement.

In the accompanying drawing Fig. I is a fragmentary view, showing in side elevation a metal conduit of typical form, with three access elements embodying our invention applied thereto; Fig. II is a view of the conduit and an applied access element in cross section and to larger scale; Fig. III is a fragmentary view, showing in elevation and to the scale of Fig. II the end of one of the clamping members included in the structure of our invention; and Fig. IV is a view in side elevation, to smaller scale than Fig. II, of a special tool that is used in cooperation with the access element structure in forming an access opening in the wall of the conduit.

Referring to the drawing, the reference numeral I is applied to a length of conduit, typical of the conduits that in known way are assembled and embedded in the concrete floor of a building, to provide an underfloor duct system for electrical service wires. heavy-walled metal tube of rectangular crosssection, with the corners rounded, as indicated'at la in Fig. II; and it is to be understood that the access element of our invention has been designed particularly for use with conduits of this sort. In Fig. I three access elements, 2, are shown assembled upon the conduit, and as presently will appear these elements are adapted to be installed' justed longitudinallyof the conduit, thus per- The conduit I consists in a` And it will be further noted that the access elements may be readily ad;l

selective locating of the elements in the assembled system.

The access element consists in a metal cup or tube which is so particularly fashioned that its wall 2a, includes three concentric cylindrical portions 2b, 2c, and 2d that are of successively decreased diameter, as shown. The portions 2b and 2c are internally threaded, severally to receive and secure in threaded engagement a collar 3 and fixture-supporting ring 4, while the inner cylindrical surface of portion 2d, contiguous with the lower rim or lip 2e of the access element, is accurately and smoothly finished for cooperation with a specialized drill, as Will presently appear.

In accordance with the invention, we provide means on the tubular or cup-shaped access element for positively locking the element upon the conduit, with its lower rim 2e centered and tightly secured upon the upper or top wall lb of the conduit. Such means consist, advantageously, in a pair of tong-like arms that are formed of relativelyv narrow (Fig. I) straps 5 of spring steel. 'I'he resilient straps are secured at their upper ends to the wall of the access element at diametrically opposite points, and, while integration of the straps with the body of the access element may be effected in numerous ways, riveting is preferred. Specifically, the side wall portion 2b of the access element is regionally embossed, as at 2f, and the two rivets 6 that secure each strap to the element are arranged with their heads nested within the pockets thus provided in the otherwise continuous threaded surface of the said Wall portion 2b of the access element. Extending downward from the rivets 6, the resilient straps 5 are so formed that they bear laterally upon the access element at points 5a and 5b; continuing downward from these points, the straps snugly embrace the side walls of the conduit I in surface-to-surface contact; and each strap is inturned at its lower end, providing a portion 5c that passes inward beneath the adjacent lower `corner la of the conduit and such inturned portion of the strap terminates in an upwardly directed, serrated edge 5d which takes purchase upon the bottom wall of the conduit. The two straps, thus formed and arranged, provide in effect a pair of resilient tongs whose medial portions frictionally embrace the sides of the conduit and Whose distal portions positively engage the bottom of the conduit and lock the access element in assembly therewith. It is im,- portant to note that mechanical security of assembly is thus obtained without any portion of the tong or clamping members being embedded in or driven into the body of the conduit. No special treatment of the metal conduit is required, tol admit of the assembly of the access element thereon, and no tools are required. These are valuable characteristics or features attending the practice of our invention. In making the assembly, the tong arms, while possessing a high degree of resiliency or spring strength, may be readily spread apart andapplied over the conduit body, and this operation is facilitated by the provision of tong arms of maximum permissive length, the arms being secured at their upper ends adjacent to the top of the access element 2. And the security, andaccuracy of centering, of the access element upon the conduit (which security and accuracy might otherwise be lost through such use of elongate tong arms 5) are preserved by sor shaping the arms that they engage'the access element at the points 5a and 5b; thatV is, the access element isV in eiect securely engaged throughout its entire vertical extent. Thus, the access element may be readily assembled and secured upon the square or rectangularsectioned metal conduit, with the lower rim 2e of the access element positively held in seated position upon the top Wall of the conduit.

If desired, tangs 5f may be struck from the bodies of the straps 5, to provide projections that are locked in concrete when the floor is cast and hardened upon the assembly.

It will be understood that, while the tong-like arms 5 positively secure the assembly, the applied access elementv may be readily adjusted longitudinally of the conduit. That is to say, Whereas the engagement of the serrated tips 5d with the bottom of the conduit is effective to prevent an accidental or unintended spreading of the arms 5 from the position of service in which they are shown in Fig. II, such tips do not prevent the intentional movement of the applied element lengthwise of the conduit. In consequence, the applied element may be inched along the conduit to any desired ultimate position of assembly.

It rwill be understood that there is no opening in the top wall of the conduit l when the access element is initially applied, and that the supporting ring 4 (sometimes known as the radius ring) is not included in the assembly. On the other hand, the collar 3 is included in the assembly, and in usual way is vertically adjusted to such position in the access element that its upper, iianged rim lies at the desired interval below the nished surface line or plane of the iloor under construction. Before the concrete isv poured a dished cover 'l of usual form is applied, to close the mouth of the access element, and in known way a screw 8, carried by the cover, is vertically adjusted to such position that the top of its head lies flush with said oor line. The screw provides in the surface of the iinished floor a marker which indicates-the exact location of the embedded access element.

When it becomes desirable to make a branch connection through the floor to the buried conduit, the concrete surrounding the marker screw 8 in the floor is cracked away, and the lid 1 upon the' access element, thus uncovered, is removed.

Next, an opening is made through the Wall .portion of the conduit exposed at the bottom of the access element, and in the drilling of this opening the portion 2d of our access element proves particularly valuable. The drill employed is of the specialized form shown in Fig. IV, which is drawn on smaller scale than Fig. II. The body of the drill consists in a cylindricalA shell 9 Whose lower edge is formed into, or carries, a circumferential line of :cutters 90. The inner cylindrical surface of portion 2d of the access element 2 is slightly greater in diameter than` the body 9 of the drill, so that the drill, ,when introducedl to the uncovered accessl element and its cutters brought to cutting engagement with the top wall of the conduit, is snugly engaged by such cylindrical surface, in much they same man-ner as a journal is engaged by its bearing. 'IhisA annular surface of portion 2d of' the access element serves accurately to center the drill, and, during the drilling operation, the drill is supported and guided, whereby the opening Ic provided thereby accurately registers with the lowermcuth of the access element.

Upon removal of the drill, the ring 4 is screwed into place, it being notedl th'atthe body of the access; element provides, between threaded wall portion 2c and drill-guiding portion 2d, a shoulder 2h against which the complementary body of the ring is tightly seated. The internal wall of the ring 4 is threaded, as shown at 4a, to receive and secure the lower end of the usual stand-pipe l0, or other xture, that extends upward from the supporting ring and provides the desired vertical passage through which the electric branch conductors (not shown) are led out in known way. Other than to the extent disclosed herein, our invention is not immediately concerned with the form of the stand-pipe, nor with special details of how the branch connection is made; it suices that the lower end of a stand-pipe be fragmentarily indicated in Fig. II, with the understanding that normally the ring 4 and stand-pipe are not included in the assembly until after the cover 1 has been removed and an opening Ic has been formed in the top wall of the conduit. There is, however, an important detail in the structure of the ring 4 that merits particular consideration. Specifically, the lower edge of the ring is of funnel shape, including a round or curved surface 4b that protects the electrical conductors (not shown) from engagement with the relatively sharp peripheral edge of the opening lc in the wall of the conduit.

More specifically, the body of the ring 4, from the shoulder 2h downward to the inner surface of the top wall Ib of the conduit, is of cylindrical form, snugly fitting the inner cylindrical surface of portion 2d of the access element and the edge of the said opening Ic. The lower edge of the ring extends downward an interval below the upper wall of the conduit, and, beginning at the edge of opening lc, the surface of the ring curves downward and inward, then upward and inward to a region 4c that defines the eiective internal diameter of the ring, and then upward and outward from such region 4c to the base of the threaded wall portion 4a of the ring. The diameter of th-e ring in the region 4c is at least equal to, and in this case is less than, the internal diameter of the stand-pipe I 0, and thus it is that the electrical conductors which are led upward from the conduit l are protected from the sharp edge of the lower end of the stand-pipe. By virtue of such refinement in structure the conductors bear only upon the round surface 4b of the ring, and at no point in the assembly do the conductors come into contact with an edge f that might tend to cut or erode the insulation with which they are covered.

It is to be understood that our invention is not to be limited to the exemplary construction described above. The appended claims dene the invention, and within the terms and intent thereof various modifications and refinements are held in contemplation, and are covered thereby.

We claim:

1. In an underoor duct system the combination of a conduit having an opening through a wall thereof, an access element having tong-like conduit-embracing arms for engaging the access element to the conduit, the said access element beingy positioned on the conduit with a peripheral edge of the access element surrounding the opening in the wall of the conduit and having a portion of its peripheral edge structure formed as a drill-guide for Vmaking the said opening, and a fixture-mounting ring engaged with the access element and extended into the said opening,

the said ring having its interior surface adjacent the said opening curved upward and inward toward the interior of the access element to provide a funnel-like mouth for drawing wires from the conduit into the access element.

2. An underfloor duct system including a metal duct approximately rectangular in cross section, an access element von the top wall of the said duct, a pair of resilient tong-like arms secured to the said access element and extended therefrom along opposite sides of the duct, terminal portions of the said arms turned toward each other yieldingly to contact the bottom wall of the duct embracingly to engage the access element to the duct, and bent portions in the said arms extended toward each other intocontact with the access element adjacent the top wall of the duct providing points of yielding deection at the lower region of the access element for the portions of Vthe said resilient arms which extend along and beneath the walls of the duct.

3. An underfloor duct system including a metal duct approximately rectangular in cross section, a tubular access element `composed of inner and outer members on the top wall ofthe duct, the inner member of the said access element being adjustable axially of the outer member thereof, a pair of yielding tong-like arms secured to the outer member of the said access element and extended therefrom along opposite sides of the duct, terminal portions of the said arms turned toward each other yieldingly to contact the bottom wall of the duct embracingly to engage the access element to the duct, and bent portions in the said arms extended toward each other into contact with the access element adjacent the top wall of the duct providing points of yielding deflection at the lower region of the access element for th-e portions of the said resilient arms whitch extend along and beneath the walls of the duc f WILLIAM C. ROBINSON. JAMES M, G. FULLMAN. 

